73 results on '"Rajeswari Roy"'
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2. Manifestation of incoherent-coherent crossover and non-Stoner magnetism in the electronic structure of Fe$_3$GeTe$_2$
- Author
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Sharma, Deepali, Ali, Asif, Bhatt, Neeraj, Chowdhury, Rajeswari Roy, Patra, Chandan, Singh, Ravi Prakash, and Singh, Ravi Shankar
- Subjects
Condensed Matter - Strongly Correlated Electrons - Abstract
Two-dimensional (2D) van der Waals ferromagnets have potential applications as next-generation spintronic devices and provide a platform to explore the fundamental physics behind 2D magnetism. The dual nature (localized and itinerant) of electrons adds further complexity to the understanding of correlated magnetic materials. Here, we present the temperature evolution of electronic structure in 2D van der Waals ferromagnet, Fe$_{3}$GeTe$_{2}$, using photoemission spectroscopy in conjunction with density functional theory (DFT) plus dynamical mean field theory (DMFT). With the appearance of quasiparticle peak and its evolution in the vicinity of Fermi energy, we unveil empirical evidences of incoherent-coherent crossover at around 125 K. DFT+DMFT results show that the quasiparticle lifetime surpasses thermal energy for temperature below 150 K, confirming incoherent-coherent crossover in the system. No appreciable change in the Fe 2$p$ core level, overall valence band spectra across the magnetic transition, and temperature dependent ferromagnetic DFT+DMFT results, provide substantial evidence for non-stoner magnetism in Fe$_{3}$GeTe$_{2}$. We elucidate the temperature dependent intimate relation between magnetism and electronic structure in Fe$_{3}$GeTe$_{2}$. Sommerfeld coefficient of $\sim$ 104 mJ mol$^{-1}$ K$^{-2}$ obtained in the low temperature limit from DFT+DMFT calculations resolve the long standing issue of large Sommerfeld coefficient ($\sim$ 110 mJ mol$^{-1}$ K$^{-2}$) obtained from specific heat measurements., Comment: to appear in Phys. Rev. B
- Published
- 2024
3. Unconventional Hall effect and its variation with Co-doping in van der Waals Fe3GeTe2
- Author
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Rajeswari Roy Chowdhury, Samik DuttaGupta, Chandan Patra, Oleg A. Tretiakov, Sudarshan Sharma, Shunsuke Fukami, Hideo Ohno, and Ravi Prakash Singh
- Subjects
Medicine ,Science - Abstract
Abstract Two-dimensional (2D) van der Waals (vdW) magnetic materials have attracted a lot of attention owing to the stabilization of long range magnetic order down to atomic dimensions, and the prospect of novel spintronic devices with unique functionalities. The clarification of the magnetoresistive properties and its correlation to the underlying magnetic configurations is essential for 2D vdW-based spintronic devices. Here, the effect of Co-doping on the magnetic and magnetotransport properties of Fe3GeTe2 have been investigated. Magnetotransport measurements reveal an unusual Hall effect behavior whose strength was considerably modified by Co-doping and attributed to arise from the underlying complicated spin textures. The present results provide a clue to tailoring of the underlying interactions necessary for the realization of a variety of unconventional spin textures for 2D vdW FM-based spintronics.
- Published
- 2021
- Full Text
- View/download PDF
4. Spin-polarized supercurrent through the van der Waals Kondo lattice ferromagnet Fe$_3$GeTe$_2$
- Author
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Rana, Deepti, R, Aswini, G, Basavaraja, Patra, Chandan, Howlader, Sandeep, Chowdhury, Rajeswari Roy, Kabir, Mukul, Singh, Ravi P., and Sheet, Goutam
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Superconductivity - Abstract
In the new van der Waals Kondo-lattice Fe$_3$GeTe$_2$, itinerant ferromagnetism and heavy fermionic behaviour coexist. Both the key properties of such a system namely a spin-polarized Fermi surface and a low Fermi momentum are expected to significantly alter Andreev reflection dominated transport at a contact with a superconducting electrode, and display unconventional proximity-induced superconductivity. We observed interplay between Andreev reflection and Kondo resonance at mesoscopic interfaces between superconducting Nb and Fe$_3$GeTe$_2$. Above the critical temperature ($T_c$) of Nb, the recorded differential conductance ($dI/dV$) spectra display a robust zero-bias anomaly which is described well by a characteristic Fano line shape arising from Kondo resonance. Below $T_c$, the Fano line mixes with Andreev reflection dominated $dI/dV$ leading to a dramatic, unconventional suppression of conductance at zero bias. As a consequence, an analysis of the Andreev reflection spectra within a spin-polarized model yields an anomalously large spin-polarization which is not explained by the density of states of the spin-split bands at the Fermi surface alone. The results open up the possibilities of fascinating interplay between various quantum phenomena that may potentially emerge at the mesoscopic superconducting interfaces involving Kondo lattice systems hosting spin-polarized conduction electrons., Comment: To appear in Physical Review B
- Published
- 2022
- Full Text
- View/download PDF
5. Anisotropic magnetotransport in the layered antiferromagnet TaFe$_{1.25}$Te$_3$
- Author
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Chowdhury, Rajeswari Roy, DuttaGupta, Samik, Patra, Chandan, Kataria, Anshu, Fukami, Shunsuke, and Singh, Ravi Prakash
- Subjects
Condensed Matter - Materials Science - Abstract
The discovery of fascinating ways to control and manipulate antiferromagnetic materials have garnered considerable attention as an attractive platform to explore novel spintronic phenomena and functionalities. Layered antiferromagnets (AFMs) exhibiting interesting magnetic structures, can serve as an attractive starting point to establish novel functionalities down to the two-dimensional limit. In this work, we explore the magnetoresistive properties of the spin-ladder AFM TaFe$_{1.25}$Te$_3$. Magnetization studies reveal an anisotropic magnetic behavior resulting in the stabilization of a spin-flop configuration for H $\perp$ (10-1) plane (i.e., out-of-plane direction). Angle-dependent longitudinal and transverse magnetoresistances show an unusual anharmonic behavior. A significant anisotropic enhancement of magnetoresistance when H $\perp$ (10-1) plane compared to H $\parallel$ (10-1) directions has been observed. The present results deepen our understanding of the magnetoresistive properties of low-dimensional layered AFMs, and point towards the possibility of utilizing these novel material systems for antiferromagnetic spintronics., Comment: 7 pages, 7 figures
- Published
- 2022
- Full Text
- View/download PDF
6. Modification of unconventional Hall effect with doping at the non-magnetic site in a 2D van der Waals ferromagnet
- Author
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Chowdhury, Rajeswari Roy, Patra, Chandan, DuttaGupta, Samik, Satheesh, Sayooj, Dan, Shovan, Fukami, Shunsuke, and Singh, Ravi Prakash
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
Two-dimensional (2D) van der Waals (vdW) magnetic materials have garnered considerable attention owing to the existence of magnetic order down to atomic dimensions and flexibility towards interface engineering, offering an attractive platform to explore novel spintronic phenomena and functionalities. Understanding of the magnetoresistive properties and their correlation to the underlying magnetic configurations is essential for 2D vdW-based spintronic or quantum information devices. Among the promising candidates, vdW ferromagnet (FM) Fe3GeTe2 shows an unusual magnetotransport behavior, tunable by doping at the magnetic (Fe) site, and tentatively arising from complicated underlying spin texture configurations. Here, we explore an alternative route towards manipulation of magnetotransport properties of a vdW FM without directly affecting the magnetic site i.e., by doping at the non-magnetic (Ge) site of Fe3(Ge,As)Te2. Interestingly, doping at the non-magnetic (Ge) site results in an unconventional Hall effect whose strength was considerably modified by increasing As concentration, possibly arising from emergent electromagnetic behavior from underlying complicated spin configurations. The present results provide a possible route to understand the intricate role played by the non-magnetic (Ge) atom towards magnetic properties of vdW FMs, and shows a novel direction towards tailoring of underlying interactions responsible for the stabilization of non trivial spin textures in 2D magnetic vdW materials., Comment: 9 pages
- Published
- 2021
- Full Text
- View/download PDF
7. Spectroscopic evidence of mixed angular momentum symmetry in non-centrosymmetric Ru$_7$B$_3$
- Author
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Datta, Soumya, Vasdev, Aastha, Ramachandran, Ranjani, Halder, Soumyadip, Motla, Kapil, Kataria, Anshu, Arushi, Chowdhury, Rajeswari Roy, Singh, Ravi Prakash, and Sheet, Goutam
- Subjects
Condensed Matter - Superconductivity - Abstract
Superconducting crystals with lack of inversion symmetry can potentially host unconventional pairing. However, till date, no direct conclusive experimental evidence of such unconventional order parameters in non-centrosymmetric superconductors has been reported. In this paper, through direct measurement of the superconducting energy gap by scanning tunnelling spectroscopy, we report the existence of both $s$-wave (singlet) and $p$-wave (triplet) pairing symmetries in non-centrosymmetric Ru$_7$B$_3$. Our temperature and magnetic field dependent studies also indicate that the relative amplitudes of the singlet and triplet components of the order parameter change differently with temperature.
- Published
- 2021
8. Unconventional Hall effect and its variation with Co-doping in van der Waals Fe3GeTe2
- Author
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Chowdhury, Rajeswari Roy, DuttaGupta, Samik, Patra, Chandan, Tretiakov, Oleg A., Sharma, Sudarshan, Fukami, Shunsuke, Ohno, Hideo, and Singh, Ravi Prakash
- Subjects
Condensed Matter - Materials Science ,Condensed Matter - Strongly Correlated Electrons - Abstract
Two-dimensional (2D) van der Waals (vdW) magnetic materials have attracted a lot of attention owing to the stabilization of long-range magnetic order down to atomic dimensions, and the prospect of novel spintronic devices with unique functionalities. The clarification of the magnetoresistive properties and its correlation to the underlying magnetic configurations is essential for 2D vdW-based spintronic devices. Here, the effect of Co-doping on the magnetic and magnetotransport properties of Fe3GeTe2 have been investigated. Magnetotransport measurements reveal an unusual Hall effect behavior whose strength was considerably modified by Co-doping and attributed to arise from the underlying complicated spin textures. The present results provide a clue to tailoring of the underlying interactions necessary for the realization of a variety of unconventional spin textures for 2D vdW FM-based spintronics., Comment: 20 pages, 6 figures
- Published
- 2020
- Full Text
- View/download PDF
9. Study of the superconducting ground state of topological superconducting candidates Ti$_{3}$X (X = Ir, Sb)
- Author
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Mandal, Manasi, P., Sajilesh K., Chowdhury, Rajeswari Roy, Singh, D., Biswas, P. K., Hillier, A. D., and Singh, R. P.
- Subjects
Condensed Matter - Superconductivity - Abstract
The topologically non-trivial band structure of A15 compounds has drawn attention owing to the possible realization of topological superconductivity. Here, we report a microscopic investigation of the superconducting ground state in A15 compound Ti$_{3}$X (X = Ir, Sb) by muon spectroscopy measurements. Zero field muon measurements have shown that time-reversal symmetry is preserved in these materials. Furthermore, specific heat and a transverse field muon spectroscopy measurement rule out any possibility to have a nodal or anisotropic superconducting gap, revealing a conventional s-wave nature in the superconducting ground state. This work classifies A15 compound Ti$_{3}$X (X = Ir, Sb) as a time-reversal preserved topological superconductor., Comment: 7 pages, 9 figures
- Published
- 2020
- Full Text
- View/download PDF
10. High spin-polarization in the low Curie temperature complex itinerant ferromagnet EuTi$_{1-x}$Nb$_x$O$_3$
- Author
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Kamboj, Suman, Roy, Deepak K., Roy, Susmita, Chowdhury, Rajeswari Roy, Mandal, Prabhat, Kabir, Mukul, and Sheet, Goutam
- Subjects
Condensed Matter - Materials Science - Abstract
The physical systems with ferromagnetism and "bad" metallicity hosting unusual transport properties are playgrounds of novel quantum phenomena. Recently EuTi$_{1-x}$Nb$_x$O$_3$ emerged as a ferromagnetic system where non-trivial temperature dependent transport properties are observed due to coexistence and competition of various magnetic and non-magnetic scattering processes. In the ferromagnetic state, the resistivity shows a $T^2$ temperature dependence possibly due to electron-magnon scattering and above the Curie temperature $T_c$, the dependence changes to $T^{3/2}$ behaviour indicating a correlation between transport and magnetic properties. In this paper, we show that the transport spin-polarization in EuTi$_{1-x}$Nb$_x$O$_3$, a low Curie temperature ferromagnet, is as high ($\sim 40\%$) as that in some of the metallic ferromagnets with high Curie temperatures. In addition, owing to the low Curie temperature of EuTi$_{1-x}$Nb$_x$O$_3$, the temperature ($T$) dependence of $P_t$ could be measured systematically up to $T_c$ which revealed a proportionate relationship with magnetization $M_s$ vs. $T$. This indicates that such proportionality is far more universally valid than the ferromagnets with ideal parabolic bands. Furthermore, our band structure calculations not only helped understand the origin of such high spin polarization in EuTi$_{1-x}$Nb$_x$O$_3$ but also provided a route to estimate the Hubbard $U$ parameter in complex metallic ferromagnets in general using experimental inputs., Comment: 5 pages, 4 figures
- Published
- 2019
- Full Text
- View/download PDF
11. Suppression of transport spin-polarization of surface states with emergence of ferromagnetism in Mn-doped Bi2Se3
- Author
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Kamboj, Suman, Das, Shekhar, Sirohi, Anshu, Chowdhury, Rajeswari Roy, Gayen, Sirshendu, Maurya, Vishal K., Patnaik, Satyabrata, and Sheet, Goutam
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Other Condensed Matter - Abstract
The surface states of topological insulators (TI) are protected by time reversal symmetry and they display intrinsic spin helicity where the momentum of the charge carriers decides their spin states. As a consequence, a current injected through the surface states becomes spin polarized and this transport spin-polarization leads to a proportionate suppression of Andreev reflection in superconductor/TI junctions. Here we show that upon doping Bi2Se3 with Mn, the transport spin-polarization is seen to be monotonically suppressed. The parent compound Bi2Se3 is found to exhibit a transport spin-polarization of about 63% whereas crystals with 10% Mn doping show transport spin-polarization of about 48%. This suppression is accompanied by an increasing ferromagnetic order of the crystals with Mn doping. Scanning tunneling spectroscopy shows that the topological protection of the surface states reduce due to Mn doping. The net measured transport spin-polarization is due to a competition of this effect with the increased magnetization on Mn doping. The present results provide important insights for the choice of magnetic topological insulators for spintronic applications., Comment: Accepted in Journal of Physics: Condensed Matter, 5 PAGES, 5 FIGURES
- Published
- 2018
- Full Text
- View/download PDF
12. Mixed type I and type II superconductivity due to intrinsic electronic inhomogeneities in the type II Dirac semimetal PdTe2
- Author
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Sirohi, Anshu, Das, Shekhar, Chowdhuri, Rajeswari Roy, Amit, Singh, Yogesh, Gayen, Sirshendu, and Sheet, Goutam
- Subjects
Condensed Matter - Superconductivity - Abstract
The type II Dirac semimetal PdTe$_2$ is unique in the family of topological parent materials because it displays a superconducting ground state below 1.7 K. Despite wide speculations on the possibility of an unconventional topological superconducting phase, tunneling and heat capacity measurements revealed that the superconducting phase of PdTe$_2$ follows predictions of the microscopic theory of Bardeen, Cooper and Shriefer (BCS) for conventional superconductors. The superconducting phase in PdTe$_2$ is further interesting because it also displays properties that are characteristics of type-I superconductors and are generally unexpected for binary compounds. Here, from scanning tunneling spectroscopic measurements we show that the surface of PdTe$_2$ displays intrinsic electronic inhomegenities in the normal state which leads to a mixed type I and type II superconducting behaviour along with a spatial distribution of critical fields in the superconducting state. Understanding of the origin of such inhomogeneities may be important for understanding the topological properties of PdTe$_2$ in the normal state., Comment: 3 Figures
- Published
- 2018
- Full Text
- View/download PDF
13. Planar Hall Effect and Quasi ‐ 2D Anisotropic Superconductivity in Topological Candidate 1T‐NbSeTe
- Author
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Patra, Chandan, primary, Agarwal, Tarushi, additional, Srivastava, Shashank, additional, Chowdhury, Rajeswari Roy, additional, Saravanan, M. P., additional, and Singh, Ravi Prakash, additional
- Published
- 2023
- Full Text
- View/download PDF
14. Unconventional Hall effect and its variation with Co-doping in van der Waals Fe3GeTe2
- Author
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Chowdhury, Rajeswari Roy, DuttaGupta, Samik, Patra, Chandan, Tretiakov, Oleg A., Sharma, Sudarshan, Fukami, Shunsuke, Ohno, Hideo, and Singh, Ravi Prakash
- Published
- 2021
- Full Text
- View/download PDF
15. Planar Hall Effect and Quasi ‐ 2D Anisotropic Superconductivity in Topological Candidate 1T‐NbSeTe.
- Author
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Patra, Chandan, Agarwal, Tarushi, Srivastava, Shashank, Chowdhury, Rajeswari Roy, Saravanan, M. P., and Singh, Ravi Prakash
- Subjects
HALL effect ,SUPERCONDUCTIVITY ,SUPERCONDUCTORS ,CONDENSED matter ,MAGNETIZATION measurement - Abstract
Superconducting topological materials have generated considerable interest in condensed matter research due to their unusual gap structures and topological properties. In this study, the normal and superconducting characteristics of a potential topological semimetal, 1T‐NbSeTe are investigated through comprehensive transport and magnetization measurements on bulk single crystals. The results suggest the topological semimetallic nature of NbSeTe, as evidenced by the observation of the planar Hall effect. Moreover, it displays quasi‐2D anisotropic superconductivity, which breaks the Pauli limit. The coexistence of the topological semimetallic nature and superconductivity of NbSeTe makes it a potential contender for topological superconductivity. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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16. Unconventional Emergent Hall Effect Phenomena and its Modification in a van der Waals Ferromagnet Fe3GeTe2
- Author
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Chowdhury, Rajeswari Roy, primary, Patra, Chandan, additional, DuttaGupta, Samik, additional, Fukami, Shunsuke, additional, and Singh, Ravi Prakash, additional
- Published
- 2023
- Full Text
- View/download PDF
17. Spin-polarized supercurrent through the van der Waals Kondo-lattice ferromagnet Fe3GeTe2
- Author
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Rana, Deepti, primary, R, Aswini, additional, G, Basavaraja, additional, Patra, Chandan, additional, Howlader, Sandeep, additional, Chowdhury, Rajeswari Roy, additional, Kabir, Mukul, additional, Singh, Ravi P., additional, and Sheet, Goutam, additional
- Published
- 2022
- Full Text
- View/download PDF
18. Ferromagnetism in Nd(Co1-xVx)2Si2 (0 ≤ x ≤ 0.5)
- Author
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Chowdhury, Rajeswari Roy, Dhara, Susmita, and Bandyopadhyay, Bilwadal
- Published
- 2014
- Full Text
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19. Magnetization Study of CoxCu1-x Nanoparticles
- Author
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Dhara, Susmita, Chowdhury, Rajeswari Roy, and Bandyopadhyay, Bilwadal
- Published
- 2014
- Full Text
- View/download PDF
20. Spin-polarized supercurrent through the van der Waals Kondo lattice ferromagnet Fe$_3$GeTe$_2$
- Author
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Deepti Rana, Aswini R, Basavaraja G, Chandan Patra, Sandeep Howlader, Rajeswari Roy Chowdhury, Mukul Kabir, Ravi P. Singh, and Goutam Sheet
- Subjects
Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter - Superconductivity ,FOS: Physical sciences - Abstract
In the new van der Waals Kondo-lattice Fe$_3$GeTe$_2$, itinerant ferromagnetism and heavy fermionic behaviour coexist. Both the key properties of such a system namely a spin-polarized Fermi surface and a low Fermi momentum are expected to significantly alter Andreev reflection dominated transport at a contact with a superconducting electrode, and display unconventional proximity-induced superconductivity. We observed interplay between Andreev reflection and Kondo resonance at mesoscopic interfaces between superconducting Nb and Fe$_3$GeTe$_2$. Above the critical temperature ($T_c$) of Nb, the recorded differential conductance ($dI/dV$) spectra display a robust zero-bias anomaly which is described well by a characteristic Fano line shape arising from Kondo resonance. Below $T_c$, the Fano line mixes with Andreev reflection dominated $dI/dV$ leading to a dramatic, unconventional suppression of conductance at zero bias. As a consequence, an analysis of the Andreev reflection spectra within a spin-polarized model yields an anomalously large spin-polarization which is not explained by the density of states of the spin-split bands at the Fermi surface alone. The results open up the possibilities of fascinating interplay between various quantum phenomena that may potentially emerge at the mesoscopic superconducting interfaces involving Kondo lattice systems hosting spin-polarized conduction electrons., To appear in Physical Review B
- Published
- 2022
21. Modification of unconventional Hall effect with doping at the nonmagnetic site in a two-dimensional van der Waals ferromagnet
- Author
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Rajeswari Roy Chowdhury, Chandan Patra, Samik DuttaGupta, Sayooj Satheesh, Shovan Dan, Shunsuke Fukami, and Ravi Prakash Singh
- Subjects
Physics and Astronomy (miscellaneous) ,General Materials Science - Published
- 2022
22. Rhizobacteria assisted phytoremediation of oily sludge contaminated sites
- Author
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Susmita Karmakar, Rajeswari Roy, Arijita Bhattacharyya, Biswajit Kar, Sanjeev Kumar, Ritu Singh, Kuldeep Bauddh, and Narendra Kumar
- Published
- 2022
23. Contributors
- Author
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Shahrukh Nawaj Alam, Mohammad Israil Ansari, null Anshumali, Tatiana Nkwah Bantec, Kuldeep Bauddh, Ram Naresh Bharagava, Arijita Bhattacharyya, Aqsa bibi, Nirmali Bordoloi, Sam Cherian, António Xavier Pereira Coutinho, Anuradha Devi, Sonal Dixit, Neha Dwivedi, Luiz Fernando Romanholo Ferreira, Joël Fontaine, Helena Freitas, Sudip Kumar Ghosh, Antara Ghosh, Abhishek Guldhe, Kiran Gupta, Neha Gupta, Khushboo Gupta, Arti Hansda, Shilpa Deshpande Kaistha, Biswajit Kar, Susmita Karmakar, Zaira Khalid, Prem Chand Kisku, Anup Kumar, Vipin Kumar, Vineet Kumar, Amit Kumar, Manoj Kumar, Sanjeev Kumar, Narendra Kumar, Raushan Kumar, Khushbu Kumari, Priyanka Kumari, Muhammad Laiq, Anissa Lounès-Hadj Sahraoui, Ying Ma, Tushar Kanti Maiti, Soumik Mitra, Sayanta Mondal, Nandkishor More, Sikandar I. Mulla, Anna Muratova, Mohammad Nisar, Rui S. Oliveira, Manisarani Patel, Krishnendu Pramanik, Gul Raheem, Robin Raveau, Rajeswari Roy, Ashish Sachan, Lala Saha, Ganesh Dattatraya Saratale, Gauri Saxena, Mehran Shirvani, Bhaskar Singh, Shreya Singh, Ritu Singh, Soni Kumari Singh, Ravi Prakash Srivastava, Ankit Abhilash Swain, Preetanshika Tracy, Olga Turkovskaya, Abid Ullah, Pramila Devi Umrao, Neha Vishnoi, Zahra Yahaghi, and Chang Zhang
- Published
- 2022
24. Anisotropic magnetotransport in the layered antiferromagnet TaFe$_{1.25}$Te$_3$
- Author
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Rajeswari Roy Chowdhury, Samik DuttaGupta, Chandan Patra, Anshu Kataria, Shunsuke Fukami, and Ravi Prakash Singh
- Subjects
Condensed Matter - Materials Science ,Physics and Astronomy (miscellaneous) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Materials Science ,Condensed Matter::Strongly Correlated Electrons - Abstract
The discovery of fascinating ways to control and manipulate antiferromagnetic materials have garnered considerable attention as an attractive platform to explore novel spintronic phenomena and functionalities. Layered antiferromagnets (AFMs) exhibiting interesting magnetic structures, can serve as an attractive starting point to establish novel functionalities down to the two-dimensional limit. In this work, we explore the magnetoresistive properties of the spin-ladder AFM TaFe$_{1.25}$Te$_3$. Magnetization studies reveal an anisotropic magnetic behavior resulting in the stabilization of a spin-flop configuration for H $\perp$ (10-1) plane (i.e., out-of-plane direction). Angle-dependent longitudinal and transverse magnetoresistances show an unusual anharmonic behavior. A significant anisotropic enhancement of magnetoresistance when H $\perp$ (10-1) plane compared to H $\parallel$ (10-1) directions has been observed. The present results deepen our understanding of the magnetoresistive properties of low-dimensional layered AFMs, and point towards the possibility of utilizing these novel material systems for antiferromagnetic spintronics., Comment: 7 pages, 7 figures
- Published
- 2022
- Full Text
- View/download PDF
25. Disorder in Co-Cu granular alloys studied by 59Co NMR
- Author
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S. Dhara, Bilwadal Bandyopadhyay, and Rajeswari Roy Chowdhury
- Subjects
010302 applied physics ,Materials science ,Field (physics) ,Analytical chemistry ,Shell (structure) ,Resonance ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,NMR spectra database ,Condensed Matter::Materials Science ,Magnetization ,Ferromagnetism ,Zero field ,0103 physical sciences ,0210 nano-technology ,Hyperfine structure - Abstract
We have performed 59Co zero field nuclear magnetic resonance (NMR) experiment at 4 K on Co x Cu 1 - x (x = 0.10, 0.32 and 0.76) nanogranular alloys. The NMR signal arises from Co rich ferromagnetic clusters formed within the Cu matrix. The analysis of NMR spectra shows that the resonance peaks arise from both fcc and hcp phases of Co. However, Co nuclei experience magnetic hyperfine field from Co only environment as well as other environments in which nearest-neighbor (NN) Co atoms are replaced by Cu. Assuming that these two environments constitute the core and the shell of the Co clusters, it is estimated using previous magnetization measurements that the contribution of core dominates in the ferromagnetism of the particles though it occupies only about 20% of the volume of Co clusters even for high Co containing alloys.
- Published
- 2019
26. Spectroscopic evidence of mixed angular momentum symmetry in non-centrosymmetric Ru$_7$B$_3$
- Author
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Ravi Pratap Singh, Ranjani Ramachandran, Soumya Datta, Soumyadip Halder, Goutam Sheet, Kapil Motla, Arushi, Rajeswari Roy Chowdhury, Anshu Kataria, and Aastha Vasdev
- Subjects
Physics ,Superconductivity ,Angular momentum ,Multidisciplinary ,Condensed matter physics ,Condensed Matter - Superconductivity ,Point reflection ,FOS: Physical sciences ,Symmetry (physics) ,Superconductivity (cond-mat.supr-con) ,Amplitude ,Pairing ,Condensed Matter::Superconductivity ,Homogeneous space ,Singlet state - Abstract
Superconducting crystals with a lack of inversion symmetry can potentially host unconventional pairing. However, till today, no direct conclusive experimental evidence of such unconventional order parameters in non-centrosymmetric superconductors has been reported. In this paper, through direct measurement of the superconducting energy gap by scanning tunnelling spectroscopy, we report the existence of both s-wave (singlet) and p-wave (triplet) pairing symmetries in non-centrosymmetric Ru$$_7$$ 7 B$$_3$$ 3 . Our temperature and magnetic field-dependent studies also indicate that the relative amplitudes of the singlet and triplet components change differently with temperature.
- Published
- 2021
- Full Text
- View/download PDF
27. Superconducting ground state of the topological superconducting candidates Ti3X ( X=Ir,Sb )
- Author
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Mandal, Manasi, primary, K. P., Sajilesh, additional, Chowdhury, Rajeswari Roy, additional, Singh, D., additional, Biswas, P. K., additional, Hillier, A. D., additional, and Singh, R. P., additional
- Published
- 2021
- Full Text
- View/download PDF
28. Unconventional Hall effect and its variation with Co-doping in van der Waals Fe3GeTe2
- Author
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Oleg A. Tretiakov, Shunsuke Fukami, Hideo Ohno, Ravi Pratap Singh, Rajeswari Roy Chowdhury, Sudarshan Sharma, Chandan Patra, and Samik DuttaGupta
- Subjects
Materials science ,Magnetoresistance ,Science ,FOS: Physical sciences ,02 engineering and technology ,01 natural sciences ,symbols.namesake ,Condensed Matter - Strongly Correlated Electrons ,Hall effect ,0103 physical sciences ,010306 general physics ,Spin-½ ,Condensed Matter - Materials Science ,Multidisciplinary ,Spintronics ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Magnetic order ,Doping ,Materials Science (cond-mat.mtrl-sci) ,021001 nanoscience & nanotechnology ,symbols ,Medicine ,van der Waals force ,0210 nano-technology - Abstract
Two-dimensional (2D) van der Waals (vdW) magnetic materials have attracted a lot of attention owing to the stabilization of long-range magnetic order down to atomic dimensions, and the prospect of novel spintronic devices with unique functionalities. The clarification of the magnetoresistive properties and its correlation to the underlying magnetic configurations is essential for 2D vdW-based spintronic devices. Here, the effect of Co-doping on the magnetic and magnetotransport properties of Fe3GeTe2 have been investigated. Magnetotransport measurements reveal an unusual Hall effect behavior whose strength was considerably modified by Co-doping and attributed to arise from the underlying complicated spin textures. The present results provide a clue to tailoring of the underlying interactions necessary for the realization of a variety of unconventional spin textures for 2D vdW FM-based spintronics., Comment: 20 pages, 6 figures
- Published
- 2020
- Full Text
- View/download PDF
29. Magnetocaloric effect study of Pr0.67Ca0.33MnO3-La0.67Sr0.33MnO3 nanocomposite
- Author
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S. Midda, I. Das, Kalipada Das, Pintu Sen, and Rajeswari Roy Chowdhury
- Subjects
010302 applied physics ,Nanocomposite ,Materials science ,Condensed matter physics ,Thermodynamics ,Nanoparticle ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Nanomaterials ,Refrigerant ,Operating temperature ,0103 physical sciences ,Magnetic refrigeration ,Antiferromagnetism ,0210 nano-technology - Abstract
The present study involves investigaton of magnetocaloric effect of Pr0.67Ca0.33MnO3-La0.67Sr0.33MnO3 nanocomposite materials above room temperature. From application point of view in magnetic refrigeration our study highlights the enhancement of operating temperature region compared to the well known La0.67Sr0.33MnO3 refrigerant material above room temperature. Comparison has also been made with the magnetocaloric properties of La0.67Sr0.33MnO3 nanomaterials. The modification of the magnetocaloric entropy changes (broadening of the temperature dependent magnetic entropy change) is addressed due to the effect of the gradual melting of antiferromagnetic charge ordered state of the Pr0.67Ca0.33MnO3 nanoparticles in such nanocomposite materials.
- Published
- 2018
30. Enhancement of magnetocaloric effect in V doped intermetallic compoundsNd(Co1−xVx)2Si2( x =0, 0.20 and 0.35)
- Author
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Bilwadal Bandyopadhyay, Rajeswari Roy Chowdhury, and S. Dhara
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,Doping ,Intermetallic ,Vanadium ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Crystallography ,Ferromagnetism ,Transition metal ,chemistry ,0103 physical sciences ,Magnetic refrigeration ,Antiferromagnetism ,Electrical and Electronic Engineering ,0210 nano-technology ,Ground state - Abstract
We report a large enhancement of magnetocaloric entropy change in vanadium substituted intermetallic compounds Nd ( Co 1 − x V x ) 2 Si 2 (x = 0.20 and 0.35). The antiferromagnetic parent compound NdCo2Si2 exhibits inverse magnetocaloric response. Upon vanadium doping, antiferromagnetic transition is gradually suppressed and there is a drastic modification of the ground state, with appearance of ferromagnetism in Nd ( Co 0.65 V 0.35 ) 2 Si 2 . Such modifications are reflected in the magnetocaloric properties of the parent and the doped compounds. In comparison to the inverse magnetocaloric response of the parent compound, the doped compound with x = 0.35 shows a conventional magnetocaloric effect that is large in magnitude compared to the parent compound. A table-like MCE in a wide-temperature range of 5–60 K have been observed in Nd ( Co 0.65 V 0.35 ) 2 Si 2 . The present study demonstrates enhancement of magnetic entropy by way of substitution at the transition metal site in these compounds.
- Published
- 2017
31. Mixed type I and type II superconductivity due to intrinsic electronic inhomogeneities in the type II Dirac semimetal PdTe
- Author
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Anshu, Sirohi, Shekhar, Das, Priyo, Adhikary, Rajeswari Roy, Chowdhury, Amit, Vashist, Yogesh, Singh, Sirshendu, Gayen, Tanmoy, Das, and Goutam, Sheet
- Abstract
The type II Dirac semimetal PdTe[Formula: see text] is unique in the family of topological parent materials because it displays a superconducting ground state below 1.7 K. Despite wide speculation on the possibility of an unconventional topological superconducting phase, tunneling and heat capacity measurements revealed that the superconducting phase of PdTe[Formula: see text] follows predictions of the microscopic theory of Bardeen, Cooper and Schrieffer for conventional superconductors. The superconducting phase in PdTe[Formula: see text] is further interesting because it also displays properties that are characteristic of type-I superconductors and are generally unexpected for binary compounds. Here, from scanning tunneling spectroscopic measurements we show that the surface of PdTe[Formula: see text] displays intrinsic electronic inhomogeneities in the normal state which leads to a mixed type I and type II superconducting behaviour along with a spatial distribution of critical fields in the superconducting state. Understanding of the origin of such inhomogeneities may be important for understanding the topological properties of PdTe[Formula: see text] in the normal state.
- Published
- 2018
32. Evidence of ferromagnetism in vanadium substituted layered intermetallic compoundsRE(Co1−xVx)2Si2( RE =Pr and Nd;0≤x≤0.35)
- Author
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Bilwadal Bandyopadhyay, Rajeswari Roy Chowdhury, and S. Dhara
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,Intermetallic ,02 engineering and technology ,Coercivity ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Magnetic susceptibility ,Electronic, Optical and Magnetic Materials ,Magnetization ,Exchange bias ,Ferromagnetism ,Ferrimagnetism ,0103 physical sciences ,0210 nano-technology ,Saturation (magnetic) - Abstract
In intermetallic compounds RECo2Si2 (RE=Pr and Nd), cobalt has been partially substituted by vanadium to obtain RE(Co1−xVx)2Si2 ( 0 ≤ x ≤ 0.35 ). The parent compounds are antiferromagnetic below about 30 K due to the ordering of localized magnetic moments that are present only on rare-earth ions, cobalt being non-magnetic in the parent compounds. The present study demonstrates that in these compounds where 3 d and 4 f ions occupy different layers in the crystal structure, V substitution and subsequent lattice expansion results in the occurrence of inequivalent magnetic ions and complex interactions that lead to multiple magnetic transitions. At temperatures around 40–50 K, the temperature dependence of magnetization indicates a ferrimagnetic transition which is accompanied by a rapid decrease in the temperature dependence of resistivity. Below temperatures ∼30 K, the samples begin to show ferromagnetic-like behavior with the appearance of a coercive field and saturation in the magnetization at magnetic fields above ∼2 T. These two magnetic transitions are indicated also by prominent λ-like peaks in specific heat measurements. At around 10 K, a sharp drop in the resistivity indicates another magnetic transition which is followed by a rapid increase in coercive field with decrease in temperature. In a magnetic field of 9 T, the latter transition shifts to a lower temperature and that leads to a positive magnetoresistance. The onset of ferromagnetism at ∼30 K is accompanied with an exchange bias field which is observed for the first time in layered intermetallic compounds. The exchange bias field increases rapidly below the transition at ∼10 K and reaches ∼16% of coercive field at 2 K.
- Published
- 2016
33. Anomalous magnetoresistance and magnetocaloric behaviour in layered intermetallic compound NdRu2Si2
- Author
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R. Rawat, Rajeswari Roy Chowdhury, Bilwadal Bandyopadhyay, and S. Dhara
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,Magnetoresistance ,Intermetallic ,02 engineering and technology ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Magnetic field ,Magnetization ,Ferromagnetism ,0103 physical sciences ,Magnetic refrigeration ,Electrical and Electronic Engineering ,0210 nano-technology ,Néel temperature - Abstract
The magnetoresistance (MR) and magnetocaloric properties of naturally occurring layered compound NdRu2Si2 with a Neel temperature TN = 24 K have been investigated in the temperature range 60 ≥ T ≥ 1.8 K. It has been shown that a high external magnetic field greatly modifies the MR properties of the compound which in its low temperature ferromagnetic state (T
- Published
- 2020
34. Suppression of transport spin-polarization of surface states with emergence of ferromagnetism in Mn-doped Bi
- Author
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Suman, Kamboj, Shekhar, Das, Anshu, Sirohi, Rajeswari, Roy Chowdhury, Sirshendu, Gayen, Vishal K, Maurya, Satyabrata, Patnaik, and Goutam, Sheet
- Abstract
The surface states of topological insulators (TI) are protected by time reversal symmetry and they display intrinsic spin helicity where the momentum of the charge carriers decides their spin states. As a consequence, a current injected through the surface states becomes spin polarized and this transport spin-polarization leads to a proportionate suppression of Andreev reflection in superconductor/TI junctions. Here we show that upon doping Bi
- Published
- 2018
35. Mixed type I and type II superconductivity due to intrinsic electronic inhomogeneities in the type II Dirac semimetal PdTe2
- Author
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Amit Vashist, Sirshendu Gayen, Tanmoy Das, Shekhar Das, Rajeswari Roy Chowdhury, Priyo Adhikary, Anshu Sirohi, Goutam Sheet, and Yogesh Singh
- Subjects
Superconductivity ,Physics ,Condensed matter physics ,Condensed Matter - Superconductivity ,Dirac (software) ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Heat capacity ,Semimetal ,Superconductivity (cond-mat.supr-con) ,Phase (matter) ,Condensed Matter::Superconductivity ,0103 physical sciences ,General Materials Science ,Microscopic theory ,010306 general physics ,0210 nano-technology ,Ground state ,Quantum tunnelling - Abstract
The type II Dirac semimetal PdTe$_2$ is unique in the family of topological parent materials because it displays a superconducting ground state below 1.7 K. Despite wide speculations on the possibility of an unconventional topological superconducting phase, tunneling and heat capacity measurements revealed that the superconducting phase of PdTe$_2$ follows predictions of the microscopic theory of Bardeen, Cooper and Shriefer (BCS) for conventional superconductors. The superconducting phase in PdTe$_2$ is further interesting because it also displays properties that are characteristics of type-I superconductors and are generally unexpected for binary compounds. Here, from scanning tunneling spectroscopic measurements we show that the surface of PdTe$_2$ displays intrinsic electronic inhomegenities in the normal state which leads to a mixed type I and type II superconducting behaviour along with a spatial distribution of critical fields in the superconducting state. Understanding of the origin of such inhomogeneities may be important for understanding the topological properties of PdTe$_2$ in the normal state., 3 Figures
- Published
- 2018
36. Large positive magnetoresistance in intermetallic compound NdCo2Si2
- Author
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S. Dhara, R. Rawat, I. Das, Rajeswari Roy Chowdhury, and Bilwadal Bandyopadhyay
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,Magnetoresistance ,Magnetic structure ,Field (physics) ,Intermetallic ,Fermi surface ,02 engineering and technology ,GIANT MAGNETORESISTANCE ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,ANTIFERROMAGNETIC METALS ,01 natural sciences ,LOW-TEMPERATURES ,Electronic, Optical and Magnetic Materials ,Magnetic field ,PRCO2SI2 ,0103 physical sciences ,Magnetic refrigeration ,Antiferromagnetism ,0210 nano-technology ,SMMN2GE2 - Abstract
The magnetic, magneto-transport and magnetocaloric properties of antiferromagnetic intermetallic compound NdCo2Si2 (T-N = 32 K) have been studied. The compound yields a positive magnetoresistance (MR) of about similar to 123% at similar to 5 K in 8 T magnetic field. The MR value is significantly large vis - a - vis earlier reports of large MR in intermetallic compounds, and possibly associated with the changes in magnetic structure of the compound. The large MR value can be explained in terms of field induced pseudo-gaps on Fermi surface. (C) 2017 Elsevier B.V. All rights reserved.
- Published
- 2018
37. Suppression of transport spin-polarization of surface states with emergence of ferromagnetism in Mn-doped Bi2Se3
- Author
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Goutam Sheet, Sirshendu Gayen, Anshu Sirohi, Satyabrata Patnaik, Shekhar Das, Suman Kamboj, V. K. Maurya, and Rajeswari Roy Chowdhury
- Subjects
Physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Spin polarization ,Spintronics ,Spin states ,Condensed matter physics ,Scanning tunneling spectroscopy ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Andreev reflection ,Condensed Matter - Other Condensed Matter ,Magnetization ,Topological insulator ,Condensed Matter::Superconductivity ,0103 physical sciences ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,General Materials Science ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Surface states ,Other Condensed Matter (cond-mat.other) - Abstract
The surface states of topological insulators (TI) are protected by time reversal symmetry and they display intrinsic spin helicity where the momentum of the charge carriers decides their spin states. As a consequence, a current injected through the surface states becomes spin polarized and this transport spin-polarization leads to a proportionate suppression of Andreev reflection in superconductor/TI junctions. Here we show that upon doping Bi2Se3 with Mn, the transport spin-polarization is seen to be monotonically suppressed. The parent compound Bi2Se3 is found to exhibit a transport spin-polarization of about 63% whereas crystals with 10% Mn doping show transport spin-polarization of about 48%. This suppression is accompanied by an increasing ferromagnetic order of the crystals with Mn doping. Scanning tunneling spectroscopy shows that the topological protection of the surface states reduce due to Mn doping. The net measured transport spin-polarization is due to a competition of this effect with the increased magnetization on Mn doping. The present results provide important insights for the choice of magnetic topological insulators for spintronic applications., Comment: Accepted in Journal of Physics: Condensed Matter, 5 PAGES, 5 FIGURES
- Published
- 2018
- Full Text
- View/download PDF
38. Temperature dependent transport spin-polarization in the low Curie temperature complex itinerant ferromagnet EuTi1−x Nb x O3
- Author
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Kamboj, Suman, primary, Roy, Deepak K, additional, Roy, Susmita, additional, Chowdhury, Rajeswari Roy, additional, Mandal, Prabhat, additional, Kabir, Mukul, additional, and Sheet, Goutam, additional
- Published
- 2019
- Full Text
- View/download PDF
39. Mixed type I and type II superconductivity due to intrinsic electronic inhomogeneities in the type II Dirac semimetal PdTe2
- Author
-
Sirohi, Anshu, primary, Das, Shekhar, additional, Adhikary, Priyo, additional, Chowdhury, Rajeswari Roy, additional, Vashist, Amit, additional, Singh, Yogesh, additional, Gayen, Sirshendu, additional, Das, Tanmoy, additional, and Sheet, Goutam, additional
- Published
- 2019
- Full Text
- View/download PDF
40. Evidence of Formation of CoxCu1-xNanoparticles with Core-Shell Structure
- Author
-
S. Dhara, Bilwadal Bandyopadhyay, and Rajeswari Roy Chowdhury
- Subjects
Core shell ,Crystallography ,Materials science ,General Physics and Astronomy ,Nanoparticle - Published
- 2015
41. Synthesis, characterization and magnetic properties of Co Cu1− (x∼0.01–0.3) granular alloys
- Author
-
S. Dhara, S. Lahiri, Rajeswari Roy Chowdhury, Bilwadal Bandyopadhyay, and P. Ray
- Subjects
Magnetization ,Paramagnetism ,Magnetic anisotropy ,Materials science ,Ferromagnetism ,Thermoremanent magnetization ,Condensed matter physics ,Analytical chemistry ,Coercivity ,Atmospheric temperature range ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Superparamagnetism - Abstract
Nanostructured CoCu granular alloys have been prepared by borohydride reduction of CuCl2 and CoCl2 salt solutions using cetyltrimethylammonium bromide (CTAB) as a surfactant. Characterization by inductively coupled plasma optical emission spectroscopy (ICPOES), X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies yields spherical particles of CoxCu1−x ( x ∼ 0.01 – 0.3 ) of average size 8–25 nm formed in a face-centered-cubic (fcc) lattice as in copper. Studies of zero-field-cooled/field-cooled (ZFC/FC) magnetization and thermoremanent magnetization (TRM) have been performed in the temperature range 4–300 K, and the results have been analyzed by independent particle model. At the lowest cobalt concentration ( x ∼ 0.01 ), the alloy is superparamagnetic and there is no blocking of magnetization down to 4 K. For all other samples, the magnetization at low magnetic field is characterized by a blocking temperature distribution which is not influenced by the Co content in samples. Study of hysteresis loops shows that the magnetization at any temperature 4–300 K is a sum of ferromagnetic (FM), superparamagnetic (SPM) and paramagnetic (PM) contributions. The FM part increases and SPM part decreases with increase in Co content. However, the values of coercivity and magnetic anisotropy constant do not depend on Co content. The results suggest that CoxCu1−x alloys are formed in a spherical core-shell type structure with cobalt being concentrated near the core of particles.
- Published
- 2015
42. Strong memory effect at room temperature in nanostructured granular alloy Co0.3Cu0.7
- Author
-
Bilwadal Bandyopadhyay, Rajeswari Roy Chowdhury, and S. Dhara
- Subjects
Condensed Matter::Materials Science ,Magnetization ,Exchange bias ,Materials science ,Magnetic domain ,Condensed matter physics ,Ferromagnetism ,Magnetic shape-memory alloy ,General Chemical Engineering ,Relaxation (NMR) ,Antiferromagnetism ,General Chemistry ,Superparamagnetism - Abstract
Magnetic studies have been performed to characterize Co0.3Cu0.7 granular alloy synthesized by chemical reduction. The alloy consists of superparamagnetic (SPM) particles with a mean size of 14 nm and a blocking temperature distribution extending to ∼380 K. Even at 4 K where the alloy is largely ferromagnetic, the average magnetic moment of cobalt is smaller than its expected value indicating that not all Co atoms contribute to ferromagnetism. A significant temperature dependent exchange bias field is obtained from above 100 K down to 2 K. These observations suggest that the particles have a Co rich SPM core, surrounded by uncompensated dilute Co spin moments at the surface. Such a distribution, with lowering of temperature, leads to the co-existence of ferromagnetic (FM) and antiferromagnetic (AFM) interactions in the core and surface regions, respectively. Also, the sample exhibits a weak spin-glass like ordering occurring at ∼7 K. The overall behavior of the system is that of an assembly of almost non-interacting magnetic nanoparticles as suggested by the study of relaxation of magnetization. If during relaxation certain external conditions are temporarily disturbed, e.g., by lowering the temperature or changing the magnetic field the magnetization also changes accordingly; but as the conditions are restored the magnetization returns to its previous value. Such magnetic ‘memory effect’ has been studied with various experimental protocols and persists strongly even at room temperature.
- Published
- 2015
43. Gateway for Alternative Protein Production
- Author
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Abhijit Mitra, Rajeswari Roy Chowdhury, Sufi a Zaman, Pavel Biswas, Mukherjee P, and Goutam Roy Chowdhury
- Subjects
Alternative protein ,Solid waste management ,Ecology ,business.industry ,Environmental science ,Environmental pollution ,General Medicine ,business ,Computer network - Published
- 2017
44. Magnetization Study of CoxCu1-x Nanoparticles
- Author
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S. Dhara, Bilwadal Bandyopadhyay, and Rajeswari Roy Chowdhury
- Subjects
Materials science ,Condensed matter physics ,Nanoparticle ,xrd pattern ,Nanoparticlrs ,Physics and Astronomy(all) ,Coercivity ,superparamagnetism ,Condensed Matter::Materials Science ,Magnetization ,Ferromagnetism ,Transmission electron microscopy ,blocking temperature ,Inductively coupled plasma atomic emission spectroscopy ,coercivity ,Inductively coupled plasma ,hysteresis loop ,Superparamagnetism - Abstract
Nanostructured CoCu granular alloys have been prepared by chemical reduction method using NaBH4 as a reducing agent and characterized by inductively coupled plasma optical emission spectroscopy (ICPOES), x-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. Zero-field cooled and field cooled (ZFC/FC) magnetization study shows a blocking temperature distribution resulting from particle size distribution which is a characteristic of superparamagnetism. Magnetization study reveals that at low Co concentration, the alloy particles are superparamagnetic. At higher Co concentration the magnetization is combination of ferromagnetism (FM) and superparamagnetism (SPM). The coercive field is independent of Co concentration.
- Published
- 2014
45. Ferromagnetism in Nd(Co1-xVx)2Si2 (0 ≤ x ≤ 0.5)
- Author
-
S. Dhara, Rajeswari Roy Chowdhury, and Bilwadal Bandyopadhyay
- Subjects
ferrimagnetic ,Materials science ,Condensed matter physics ,Magnetic moment ,Intermetallic ,Physics and Astronomy(all) ,Magnetic field ,Crystallography ,Hysteresis ,x-ray diffraction ,Ferromagnetism ,Ferrimagnetism ,ferromagnetic ,Intermetallic compounds ,X-ray crystallography ,antiferromagnetic ,Antiferromagnetism ,hysteresis loop - Abstract
Magnetic properties of R(Co 1-x V x ) 2 Si 2 (R = Nd; 0 ≤ x ≤ 0.5) compounds have been investigated by magnetometric measurements. The compounds were prepared by arc melting and characterized using powder x-ray diffraction studies. The parent compound NdCo 2 Si 2 is antiferromagnetic. Cobalt, which does not carry any magnetic moment in these compounds has been substituted by vanadium. The V doped samples exhibit ferrimagnetic behaviour. Magnetizations measured at 4 K tend to saturate at high magnetic fields. The hysteresis loops and coercive fields suggest ferromagnetism occurring below ∼ 20 K. Analysis suggests occurrence of 3 d localized moments as a result of V substitution.
- Published
- 2014
46. Temperature dependent transport spin-polarization in the low Curie temperature complex itinerant ferromagnet EuTi1−x Nb x O3
- Author
-
Susmita Roy, Prabhat Mandal, Goutam Sheet, Rajeswari Roy Chowdhury, Suman Kamboj, Deepak Kumar Roy, and Mukul Kabir
- Subjects
Materials science ,Condensed matter physics ,Spin polarization ,Scattering ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Condensed Matter::Materials Science ,Magnetization ,Ferromagnetism ,Electrical resistivity and conductivity ,0103 physical sciences ,Curie ,Curie temperature ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,010306 general physics ,0210 nano-technology ,Electronic band structure - Abstract
The physical systems with ferromagnetism and 'bad' metallicity hosting unusual transport properties are playgrounds of novel quantum phenomena. Recently EuTi1-x Nb x O3 emerged as a ferromagnetic system where non-trivial temperature dependent transport properties are observed due to coexistence and competition of various magnetic and non-magnetic scattering processes. In the ferromagnetic state, the resistivity shows a T 2 temperature dependence possibly due to electron-magnon scattering and above the Curie temperature [Formula: see text], the dependence changes to T 3/2 behaviour indicating a correlation between transport and magnetic properties. In this paper, we show that the transport spin-polarization ([Formula: see text]) in EuTi1-x Nb x O3, a low Curie temperature ferromagnet, is as high (∼40%) as that in some of the metallic ferromagnets with high Curie temperatures. In addition, owing to the low Curie temperature of EuTi1-x Nb x O3, the temperature (T) dependence of [Formula: see text] could be measured systematically up to [Formula: see text] which revealed a proportionate relationship with magnetization [Formula: see text] versus T. This indicates that such proportionality is far more universally valid than the ferromagnets with ideal parabolic bands. Furthermore, our band structure calculations not only helped to understand the origin of such high spin polarization in EuTi1-x Nb x O3 but also provided a route to estimate the Hubbard U parameter in complex metallic ferromagnets in general using experimental inputs.
- Published
- 2019
47. Effect of Vanadium Substitution of Cobalt in NdCo2Si2
- Author
-
S. Dhara, Bilwadal Bandyopadhyay, and Rajeswari Roy Chowdhury
- Subjects
Materials science ,chemistry ,Substitution (logic) ,Inorganic chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Vanadium ,Cobalt - Published
- 2015
48. Observation of resistivity minimum at low temperature inCoxCu1−x(x∼0.17–0.76) nanostructured granular alloys
- Author
-
S. Dhara, Bilwadal Bandyopadhyay, and Rajeswari Roy Chowdhury
- Subjects
Materials science ,Condensed matter physics ,Alloy ,chemistry.chemical_element ,02 engineering and technology ,engineering.material ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetic field ,Metal ,chemistry ,Electrical resistivity and conductivity ,visual_art ,0103 physical sciences ,Content (measure theory) ,visual_art.visual_art_medium ,engineering ,Magnetic alloy ,010306 general physics ,0210 nano-technology ,Cobalt - Abstract
Electrical resistivity of nanostructured granular alloys ${\mathrm{Co}}_{x}{\mathrm{Cu}}_{1\ensuremath{-}x}$ ($x\ensuremath{\sim}0.01$--$0.76$) prepared by the chemical reduction method is investigated in the temperature range 2--300 K. The samples with a low cobalt content of $x\ensuremath{\le}0.1$ show a metallic resistivity behavior. For samples with a higher cobalt content, $x\ensuremath{\ge}0.17$, the resistivity shows a minimum. The minimum becomes more pronounced as Co content ($x$) increases and also as the temperature of minimum resistivity, ${T}_{\text{min}}$, increases with $x$. The resistivity minimum is obtained in this magnetic alloy system even for a cobalt concentration as high as $\ensuremath{\sim}76%$. Application of an external magnetic field has a negligible effect on the resistivity behavior. Detailed analysis suggests that the low-temperature upturn in resistivity most probably arises due to elastic electron-electron interaction (the quantum-interference effect). Magnetic measurements at 4 K on the same samples show the absence of long-range magnetic interaction and evidence of increasing magnetic disorder as $x$ increases beyond $\ensuremath{\sim}10%$. Combining the results of the two types of measurements, a model of formation of these alloy particles involving random clusters of Co atoms within the Cu matrix has been proposed.
- Published
- 2016
49. Kondo effect in CoxCu1-x granular alloys prepared by chemical reduction method
- Author
-
Bilwadal Bandyopadhyay, S. Dhara, and Rajeswari Roy Chowdhury
- Subjects
Metal ,Materials science ,Condensed matter physics ,Electrical resistivity and conductivity ,Scattering ,Impurity ,Reducing agent ,visual_art ,visual_art.visual_art_medium ,Kondo effect ,Atmospheric temperature range ,Magnetic field - Abstract
Nanostructured CoCu granular alloys CoxCu1-x (x ≤ 0.3) have been prepared by chemical reduction method using NaBH4 as a reducing agent. Electronic transport properties are studied in the temperature range 4-300 K. Resistance exhibits a metallic behavior below room temperature and draws a minimum near 20 K in all the samples except in Co0.3Cu0.7. This low temperature resistivity minimum diminishes with applied magnetic field. There is also a logarithmic temperature dependence of resistivity at temperatures below 20 K. This phenomenon indicates a Kondo-like scattering mechanism involving magnetic Co impurity spin clusters in Cu host.
- Published
- 2015
50. Crossover from antiferro-to-ferromagnetism on substitution of Co by V in RE(Co1-xVx)2Si2 (0 ≤ x ≤ 0.35)
- Author
-
Bilwadal Bandyopadhyay, Rajeswari Roy Chowdhury, and S. Dhara
- Subjects
Magnetization ,Materials science ,Exchange bias ,Atomic radius ,Ferromagnetism ,Condensed matter physics ,Magnetoresistance ,Ferrimagnetism ,Antiferromagnetism ,Magnetic susceptibility - Abstract
In PrCo2Si2 and NdCo2Si2, Co has been partially substituted by V. Vanadium having a larger atomic radius than cobalt, the substitution results in a negative pressure affecting the magnetic properties of the compound. The samples RE(Co1-xVx)2Si2 (RE = Pr, Nd; x = 0, 0.20, 0.35) were prepared by melting the corresponding elements in arc furnace and characterized using x-ray diffraction. Magnetometric measurements show that the parent compounds PrCo2Si2 and NdCo2Si2 are antiferromagnetic, as reported. With doping, ferrimagnetic behaviour is observed from temperature dependence of inverse susceptibility at about 50 K. At lower than 30 K, the magnetizations tend to saturate at high fields. From the field dependence of magnetization, the hysteresis loops and also coercive fields as observed, the samples exhibit ferromagnetism below ∼ 30 K. Exchange bias effect is also observed in the high V containing sample. The specific heat studies of the samples show transitions consistent with the magnetization data. Pr(Co...
- Published
- 2015
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